Hawkin
/
arangodb
mirror of https://gitee.com/bigwinds/arangodb
1
0
Fork 0
Code Issues Projects Releases Wiki Activity

Merge branch 'devel' of github.com:arangodb/arangodb into devel

This commit is contained in:
Michael Hackstein 2016-05-03 14:24:07 +02:00
parent e068b4e20e 236ba5cd04
commit c46a818232
1 changed files with 0 additions and 73 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

73
Documentation/Books/Users/Indexing/Cap.mdpp
View File

@ -1,73 +0,0 @@
!CHAPTER Cap Constraint
!SUBSECTION Introduction to Cap Constraints
This is an introduction to ArangoDB's size restrictions aka cap constraints for
collections.
It is possible to restrict the size of collections. If you add a document and
the size exceeds the limit, then the least recently created or updated document(s)
will be dropped. The size of a collection is measured in the number of
active documents a collection contains, and optionally in the total size of
the active documents' data in bytes.
It is possible to only restrict the number of documents in a collection, or to
only restrict the total active data size, or both at the same time. If there are
restrictions on both document count and total size, then the first violated
constraint will trigger the auto-deletion of "too" old documents until all
constraints are satisfied.
Using a cap constraint, a collection can be used as a FIFO container, with just
the newest documents remaining in the collection.
For example, a cap constraint can be used to keep a list of just the most recent
log entries, and at the same time ensure that the collection does not grow
indefinitely. Cap constraints can be used to automate the process of getting rid
of "old" documents, and so save the user from implementing own jobs to purge
"old" collection data.
!SECTION Accessing Cap Constraints from the Shell
<!-- js/server/modules/@arangodb/arango-collection.js-->
ensures that a cap constraint exists
`collection.ensureIndex({ type: "cap", size: size, byteSize: byteSize })`
Creates a size restriction aka cap for the collection of `size`
documents and/or `byteSize` data size. If the restriction is in place
and the (`size` plus one) document is added to the collection, or the
total active data size in the collection exceeds `byteSize`, then the
least recently created or updated documents are removed until all
constraints are satisfied.
It is allowed to specify either `size` or `byteSize`, or both at
the same time. If both are specified, then the automatic document removal
will be triggered by the first non-met constraint.
Note that at most one cap constraint is allowed per collection. Trying
to create additional cap constraints will result in an error. Creating
cap constraints is also not supported in sharded collections with more
than one shard.
Note that this does not imply any restriction of the number of revisions
of documents.
**Examples**
Restrict the number of document to at most 10 documents:
@startDocuBlockInline collectionEnsureCapConstraint
@EXAMPLE_ARANGOSH_OUTPUT{collectionEnsureCapConstraint}
~db._create('examples');
db.examples.ensureIndex({ type: "cap", size: 10 });
for (var i = 0; i < 20; ++i) { var d = db.examples.save( { n : i } ); }
db.examples.count();
~db._drop('examples');
@END_EXAMPLE_ARANGOSH_OUTPUT
@endDocuBlock collectionEnsureCapConstraint